SYNTHESIS OF THE RESEARCH LITERATURE 11 



Fig. 3 Eh-pH diagram of stability fields for various plutonium species. Circled numbers 

 represent lines of transition from one oxidation state to another and approximate the 

 line of equilibrium between the regions in which plutonium may be susceptible to 

 change by changing Eh or pH under the conditions specified. Reactions that are not 

 considered may also occur and contain kinetic parameters of great importance. (See also 

 Raiand Serne, 1977.) 



Because the H2O-O2 couple is relatively insensitive to small changes in the partial 

 pressure of oxygen, Pu02^ is thermodynamic ally stable in solution until the concentra- 

 tion of dissolved oxygen is essentially zero. This diagram is different from those presented 

 by Polzer (1971), v^hich indicated that PUO2 is stable. Such differences reflect the 

 uncertainty in many of the values of the relevant equilibrium constants and the choice of 

 complexes considered. However, as Bondietti and Sweeton (1977) and Pourbaix (1966) 

 have stressed, the results of these calculations are only valid for the stated conditions. In 

 the formation of complexes with the 0H~ ion and other natural ligands, the effect of 

 insoluble compounds (such as phosphates) and the presence of natural reducing agents 

 must be considered. 



